[Montrealgrl]

hi guys
I'm a complete newbie when it comes to dogs so I'm hoping I could pick your brains where this issue is concerned.
My dog was castrated on Friday (and he hadn't had anything to eat until they finished his surgery in the afternoon) and they kept him overnight until Saturday morning just to keep an eye on him. They did a blood workup on him before the surgery and informed us that everything was fine. They also took out two of his baby teeth when he was there without telling us.
He seemed perfectly fine, albeit a little quiet, yesterday. He seemed quite playful and was affectionate as usual.
However, today (Sunday), he has had a very bad diarrhea and has had loose stool 4 times since this morning (it is currently 3 p.m.).
I would have definitely taken him to his vet hospital, but when I call, they are closed. I managed to get a secretary on the phone who tells me since this isn't a life or death issue, I should just call during regular business hours. However, I really don't know if this is something normal and even she wasn't able to answer me on that one. He still seems quite playful, so I don't know if he is just good at hiding his discomfort or if everything is normal.
Please let me know if you guys know anything or have had a similar experience. I am very scared (as I'm sure any of you might be when your baby is concerned). I was thinking that I am doing the responsible thing by castrating him but now I'm afraid that I've caused more issues by making my baby undergo this experience. Is it possible that this is just the after-effects of the anesthesia drug?